As Lake Superior gradually warms up this spring and the fishing heats up, too, fisheries biologists are asking anglers to pay closer attention to their catch.

Steelhead rainbow trout and coho salmon are cousins of a sort, both in the Salmonidae family. They look close enough alike that some anglers are keeping steelhead to kill and eat thinking they are coho.

That’s a problem when steelheads are highly prized and protected. In Wisconsin waters of Lake Superior only one steelhead is allowed per day for anglers to keep and it has to be at least 26 inches long to keep. In Minnesota waters of the big lake, anglers must release all wild steelhead caught. (Only steelhead with a clipped adipose fin on their rear top of their back may be kept.)

But up to five coho salmon can be kept each day in both states. And because coho usually don’t get really big, and because they taste great, many are kept smaller than 26 inches. That means anglers who are misidentifying fish are not only keeping too many steelhead but they are keeping steelhead that are legally too small to keep.

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It doesn’t do much good to have protective rules on steelhead if anglers are keeping them thinking they are coho, said Paul Piszczek, senior fisheries biologist for the Wisconsin Department of Natural Resources stationed in Superior.

“I was nosing around through the most recent creel survey (of what anglers catch) and noticed that there were quite a few steelhead showing up,” Piszczek said. “That shouldn't be happening. It really looks like they think they’re keeping coho when in fact they’re keeping steelhead.”

Cory Goldsworthy, Lake Superior Area Fisheries Supervisor for the Minnesota DNR based in French River, said misidentification of trout and salmon has always been an issue at some level on the big lake and its tributary rivers but may be more of an issue as novice Lake Superior anglers venture out onto the big lake who have less experience catching Great Lakes trout and salmon.

“It’s always a concern of ours. Especially for anglers who haven’t caught a lot of them,’’ Goldsworthy said.

Piszczek said the problem isn’t big enough to have a biological impact on the steelhead population, which seems to be holding its own.

“It’s more that I think we can do a better job of educating anglers,’’ he said.

John Krull, Wisconsin conservation warden based in Superior, agreed.

“It’s been a problem as long as I can remember, or maybe not a problem but an issue … Somebody catches a silvery fish and it goes in the live well as a coho, whether it really is or not,” Krull said. “Whether it’s on purpose or by accident, it happens.”

Tips of the tail (and mouth)

Veteran Lake Superior anglers can identify a steelhead by their general appearance. Steelhead caught on the big lake are usually hefty, bigger than three pounds, and almost always jump during the fight. Coho tend to be three pounds or smaller and don’t jump as much.

Unlike salmon, steelhead also don’t easily lose their scales when they are flopping on the floor of the boat or being handled.

If you still aren’t sure, check the tail. Steelhead have a mostly straight or square back edge to the tail. Coho have a more pronounced fork or V-shape to the back of the tail.

Perhaps the easiest way to quickly identify a steelhead is to check the color of the inside of its mouth. The inside of a steelhead’s mouth is white. The inside of any coho or chinook (king) salmon’s mouth is dark gray or black.

Another way to tell the difference is by the anal fin. The steelhead has the shortest anal fin. If you push down the tip of the fin with your finger, it will fall beyond the base of the fin. Do the same with a coho anal fin and the tip will fall beyond the midpoint of the fin. Chinook have the longest anal fin.

The coloration of the fish is different, too. The steelhead tail has many small spots arranged in distinct rows. The coho has some large spots, mostly on the upper half. The chinook has more large spots, primarily at the base of the tail, but they are not arranged in rows.

Good steelhead population returns to Brule River

The fall 2019 run of steelhead trout up Wisconsin’s Bois Brule River, one of the few actual places fish can be counted, was a good one at 6,497. A remote camera captures every fish swimming past the lamprey barrier on the lower river. That’s up from the average of 5,000-6,000 steelhead in recent years and well ahead of the 2011 to 2015 period when annual runs were below 3,000 in some cases. But even 2019 is below the 2002-2010 period which saw runs above 8,000 and even 9,000 fish per year.

Biologists are seeing consistent lengths and weight for the recent year classes, Piszczek said, noting Lake Superior appears to be providing enough food for the trout to eat during the lake portion of their lives.

Lake Superior fishing regulations

Minnesota waters

Wild, unclipped steelhead rainbow trout — Catch and release only.

Stocked, clipped rainbow trout, steelhead or Kamloops — Daily and possession limit of three, minimum size 16”.

Brook trout and splake — Daily and possession limit of 1 with a minimum size of 20”.

Brown trout — Daily and possession limit of 5 with only one over 16”.

Lake trout — Daily and possession limit of 3.

Salmon — Daily and possession limit of 5, all types.

Walleye — Daily and possession limit of 2, minimum length of 15”.

You must have a Minnesota fishing license and trout stamp to fish in Minnesota water of Lake Superior. For complete regulations go to www.dnr.state.mn.us and search fishing regulations.

Wisconsin waters

Trout — steelhead rainbow trout, brown, brook or splake — Daily and possession limit of 5, of which only one can be a rainbow and only one can be a brook trout. Minimum size for rainbow is 26” and for brown trout and splake is 15”.

Lake trout — Daily and possession limit of 3, 15-inch minimum and only one may be longer than 25”.

Salmon, all types — Daily and possession limit of 5.

Walleye — Daily and possession limit of 5, minimum size 15” and only one may be over 20”

You must have a Wisconsin fishing license and trout stamp to fish on Wisconsin waters of Lake Superior. For complete regulations go to dnr.wi.gov and search fishing regulations.